The invention relates to instruments for measuring flow in pipes, and specifically to such an instrument that mounts on a pipe.
Flowmeters for measurement of flow through pipes may be divided into in-line types, in which the flowmeter interrupts the pipe, insertion types, in which a portion of the meter projects through the wall of the pipe, and external types, with which the pipe remains intact. Typically, insertion meters attach to the wall of the pipe at the point of entry, often by means of a fitting that is welded into the wall of the pipe. Consequently, the exact location of the sensing element within the pipe is dependent on the workmanship of the person installing the fitting, and this may compromise the accuracy of the measurement. Insertion flowmeters of the thermal type, which typically require a heated element and an unheated element, normally are designed to have the probes enter the pipe through a single opening. This requires that the hole in the pipe be large enough to accommodate both elements, and it constrains the spacing of the elements.
This invention features a flowmeter for installation in existing compressed-air distribution systems. As compared with available flowmeters it provides advantages of low cost and ease of installation.
The flowmeter operates on the well-known thermal principal by which one probe is heated and maintained warmer than a second probe, the amount of heat required to maintain the temperature difference being a measure of the fluid mass velocity. It incorporates novel features, primarily aimed at facilitating its installation. First, since the probes project individually into the pipe through separate holes, the holes that must be drilled are small, and the probes may be widely spaced to minimize interaction, particularly at low flow rates. Second, since the probes are located with reference to the outside surface of the pipe, their position is not dependent on the location of a fitting welded into the pipe. Further, since sealing means are incorporated into the device and it clamps securely onto the pipe, it can be installed without cutting or welding the pipe or adding fittings.
One embodiment of the inventive flowmeter consists of two probes that project through drilled holes into a pipe, two split rings encircling the pipe in which the probes are mounted, and a control enclosure mounted on the rings. The rings resemble well-known shaft collars, each consisting of two halves that are pulled together by screws and thereby clamped onto a cylindrical surface. Each probe is mounted in a hole drilled in the corresponding ring. The control enclosure is attached to the rings with screws, and the wires from the probes pass through the rings and directly into the enclosure. A gasket is placed around each probe, between the ring and the pipe.
A second embodiment of the flowmeter consists of two probes projecting through drilled holes into a pipe, a single split ring encircling the pipe in which the probes are mounted, and a control enclosure mounted on that ring. In other respects the second embodiment resembles the first.